The present invention relates to apparatus used in steam-light hydrocarbon reforming, and particularly to tubes used in steam-light hydrocarbon reforming furnaces.
Hydrogen for use in ammonia synthesis, methanol synthesis or hydrocracking plants, is frequently produced in a process using the following reforming reaction: EQU 2H.sub.2 0+CH.sub.4 catalyst 4H.sub.2 +CO.sub.2
the hydrocarbon can be methane as shown above, or other light hydrocarbons, including naphtha. The catalyst over which the reaction is carried out, e.g., nickel on an inert support, is contained in vertical tubes which are supported in a furnace frequently called a "reforming furnace". Reforming furnaces are schematically shown in the process flow diagrams of U.S. Pat. Nos. 3,264,066 and No. 3,382,044.
The tubes extend vertically in the reforming furnace with reactants being fed via a manifold to one end of the set of tubes and product-rich gases being withdrawn from the other end of the tubes. Because the reforming reaction occurs at a high temperature and is endothermic, heat must be supplied to the tubes to heat the reactants. The reaction is carried out in the tubes at a high temperature of about 1500.degree. F. and a pressure of about 150 to 450 psig. Because of the elevated temperature and pressure, the tubes are under considerable stress. Because of this stress, it has been necessary to replace tubes frequently, as they have developed fissures or other imperfections or breaks. Replacement of tubes is expensive and sometimes causes or prolongs costly plant downtime.